Seat belt tension prediction

ABSTRACT

A vehicle seat belt tension prediction system and method comprises an accelerometer having an output signal responsive to vertical acceleration of the vehicle, a seat weight sensor having an output signal responsive to the force exerted by a mass resting on the seat, and a processor means for calculating seat belt tension. The processor is provided with a plurality of inputs operatively coupled to the accelerometer output and seat weight sensor output. Suitable programming is provided to instruct the processor to calculate the average mass resting on the vehicle seat and predict the force that should be exerted on the seat for a measured level of vertical acceleration assuming zero belt tension. The processor then compares the actual force measured by the seat weight sensor with the predicted force to determine seat belt tension thereby obviating the necessity of complex hardware in physical contact with the seat belt system.

CROSS REFERENCE TO RELATED APPLICATIONS

More than one reissue application has been filed for reissue of U.S.Pat. No. 6,161,439. In particular, two applications for reissue of U.S.Pat. No. 6,161,439 have been filed: Reissue application Ser. No.10/326,170, filed Dec. 19, 2002, and the present reissue application,which is a divisional reissue application thereof.

The instant application claims the benefit of U.S. ProvisionalApplication Ser. No. 60/046,233, filed May 12, 1997.

Co-pending U.S. application Ser. No. 08/993,701 entitled “Seat WeightSensor Having Fluid Filled Bladder”, filed on Dec. 18, 1997, claimingbenefit of U.S. Provisional Application Ser. No. 60/032,380 filed onDec. 19, 1996, and assigned to the assignee of the instant inventiondiscloses a hydrostatic weight sensor comprising a fluid filled bladderand a pressure sensor for sensing the weight of an occupant in a vehicleseat for controlling a safety restraint system. U.S. application Ser.No. 08/993,701 also discloses a load distributor for distributing loadsacross the load bearing surface of the hydrostatic weight sensor. U.S.application Ser. No. 08/993,701 and U.S. Provisional Application Ser.No. 60/032,380 are incorporated herein by reference.

Co-pending U.S. application Ser. No. 09/003,672 entitled “AutomotiveSeat Weight Sensing System”, filed on Jan. 7, 1997, claiming benefit ofU.S. Provisional application Ser. No. 60/034,018 filed on Jan. 8, 1997,and assigned to the assignee of the instant invention discloses a seatweight sensing system comprising a plurality of hydrostatic weightsensors each of which is in accordance with U.S. application Ser. No.08/993,701. U.S. application Ser. No. 09/003,672 and U.S. provisionalapplication Ser. No. 60/034,018 are incorporated herein by reference.

Co-pending U.S. application Ser. No. 09/003,870 entitled “Vehicle SeatSensor Having Self-Maintaining Air Bladder”, filed on Jan. 7, 1997,claiming benefit of U.S. provisional application Ser. No. 60/035,343filed on Jan. 16, 1997, and assigned to the assignee of the instantinvention discloses an apparatus for automatically maintaining thesupply of sensing fluid in a hydrostatic weight sensor. U.S. applicationSer. No. 09/003,870 and U.S. Provisional Application Ser. No. 60/035,343are incorporated herein by reference.

Co-pending U.S. application Ser. No. 09/003,868 entitled “Seat WeightSensor with Means for Distributing Loads”, filed on Jan. 7, 1997,claiming benefit of U.S. Provisional Application Ser. No. 60/058,084filed on Sep. 4, 1997, and assigned to the assignee of the instantinvention discloses a load distributor for distributing sensed loadacross the load bearing surface of a hydrostatic weight sensor. U.S.application Ser. No. 09/003,868 and U.S. Provisional Application Ser.No. 60/058,084 are incorporated herein by reference.

Co-pending U.S. application Ser. No. 09/003,673 entitled “Seat WeightSensor Having Self-Regulating Fluid Filled Bladder”, filed on Jan. 7,1997, claiming benefit of U.S. Provisional Application Ser. No.60/058,119 filed on Sep. 4, 1997, and assigned to the assignee of theinstant invention discloses a hydrostatic weight sensor having a meansfor automatically regulating the amount of sensing fluid therein. U.S.application Ser. No. 09/003,673 and U.S. Provisional Application Ser.No. 60/058,119 are incorporated herein by reference.

Co-pending U.S. application Ser. No. 09/003,746 entitled “Seat WeightSensor Using Fluid Filled Tubing”, filed on Jan. 7, 1997, claimingbenefit of U.S. Provisional Application Ser. No. 60/065,986 filed onNov. 14, 1997, and assigned to the assignee of the instant inventiondiscloses a hydrostatic weight sensor incorporating a fluid filled tube.U.S. application Ser. No. 09/003,746 and U.S. Provisional ApplicationSer. No. 60/065,986 are incorporated herein by reference.

Co-pending U.S. application Ser. No. 09/003,744 entitled “Low ProfileHydraulic Seat Weight Sensor”, filed on Jan. 7, 1997, claiming benefitof U.S. Provisional Application Ser. No. 60/065,832 filed on Nov. 14,1997, and assigned to the assignee of the instant invention discloses ahydrostatic weight sensor constructed from plates or sheets ofsemi-rigid material and filled with a liquid, grease, Bingham fluid orthixotropic material. U.S. application Ser. No. 09/003,744 and U.S.Provisional Application Ser. No. 60/065,832 are incorporated herein byreference.

TECHNICAL ART

The instant invention relates generally to automotive passengerrestraint systems and more specifically to a system and method forpredicting seatbelt tension in a vehicle utilizing a seat weight sensorand an accelerometer.

BACKGROUND OF THE INVENTION

Automotive manufacturers and the National Highway Transportation SafetyAssociation are investigating methods to disable vehicle air bags insituations where they may cause more harm than good. Typically, airbagshave been developed to deploy with enough force to restrain a 175 lb.adult in a high velocity crash. Deployment of the same air bags whenchildren are seat occupants may cause serious injury due to the forcegenerated upon inflation of the bag.

As a result, seat weight sensors and systems are being developed in anattempt to determine when the passenger seat occupant is a child. Suchsystems should identify when the occupant is small, or even when a childis in a rear facing infant seat, a forward facing child seat or abooster seat. Occupant weight measurement when a child seat is presentis further complicated by the downward force applied to the child seatby the tension of a seat belt. When a child seat is strapped tightly,the seat belt forces the child seat into the vehicle seat and can bagdeployment when children or infants are present in the seat.

A variety of methods have been used for seat belt tension measurement.Copending U.S. Provisional Application Ser. No. 60/067,071 entitled“Villari Effect Seat Belt Tension Sensor”, and copending U.S.Provisional Application Ser. No. 60/070,319 entitled “CompressiveVillari Effect Seatbelt Tension Sensor”, both assigned to the assigneeof the instant invention, disclose two seat belt tension measurementsystems utilizing sensors that operate on the principle known as theVillari effect. The Villari effect refers to the tendency of certainmaterials with magnetostrictive properties to inhibit or enhance thestrength of an electromagnetic field within the material when thematerial is being subjected to compression or tensile stress. Bymeasuring the field strength in magnetostrictive material placed in linewith a seat belt mechanism, for example in a seat belt latch or a seatbelt retractor, the relative tension in the belt may be calculated.

Furthermore, belt deflection techniques which guide a seat belt througha mechanical system that forces the belt out of a straight line whenthere is low tension have been used. Under high tension the seat beltforces the displacement of a mechanical deflector. This force may thenbe sensed utilizing an electromechanical switch. Tension measurementmechanisms have also been incorporated in the buckle of the seat belt.In one embodiment, a sliding buckle is biased back with a spring. Whenthe belt is under heavy tension, the buckle pulls forward to control aswitch that provides feedback to a vehicle processor.

The aforementioned seat belt tension measurement methods suffer from anumber of disadvantages. Initially, a great number of additional partsare required for seat belt retractors or buckle configurations. Thisadds complexity (and therefore cost) to vehicle assembly and providesfor considerable difficulty in retrofitting existing vehicles.Additionally, several of the aforementioned tension systems provide onlya threshold level of tension detection.

The present invention may be used to detect whether the seat belt isunder high tension thereby denoting that an infant seat is present.Furthermore, significant tension in the belt can be predicted withoutresorting to the complex instrumentation required to measure actual belttension. Known belt tension measurement systems that directly contactthe seat belt require additional hardware and sensors that increasecomponent count and vehicle assembly complexity.

SUMMARY OF THE INVENTION

The instant invention overcomes the aforementioned problems by providinga seat belt tension prediction system employing an accelerometer and aseat weight sensor to accurately determine the tension in a vehicle seatbelt and thereby discriminate between the presence of a tightly beltedchild seat or other object and an adult occupant.

The instant invention measures the “bounce”, or vertical acceleration,experienced by a weight on a seat weight measurement means by monitoringan accelerometer that is rigidly mounted to the vehicle seat. The bouncecan be thought of as the temporary acceleration of the weight on theseat caused by the vehicle traversing bumps or holes in the road. Thisroad-induced bounce causes oscillations in the force acting upon theseat that may be measured by a seat weight sensor.

A “free” or unbelted mass positioned on a vehicle seat will bounce upand down on the seat and may, for example, completely lose contact withthe seat in extreme cases. The weight sensor would correspondinglyinterpret this extreme case as a “spike” of zero force acting on theseat. Usually, however, the output signal produced by the weight sensorwill oscillate with a small amplitude that is dependent upon the totalmass acting upon the seat and the amplitude of the road-induced vehiclebounce. When the force acting downwardly on the seat is increased due tothe tension in a tight seat belt, the amplitude of oscillation of anoutput signal produced by the weight sensor will be reduced because acomponent of the force caused by the tension in the seatbelt isconstant. Accordingly, a seatbelt tension may be calculated bydetermining the vertical acceleration of the vehicle and the variationin force exerted on the seat as measured by the seat weight sensor.

A conventional accelerometer provides an electrical signal proportionalto the vertical acceleration that the seat, and therefore the mass inthe seat, experiences. When actual vertical acceleration is compared tothe oscillating output signal produced by the weight sensor, a measureof the force on the seat attributable to the tension in the seat beltmay be calculated. The road-induced vertical acceleration acting on thevehicle is used to predict the amount of force exerted downwardly on theseat given that no seat belt tension is present.

A conventional microprocessor is adapted to accept output signals fromthe accelerometer and the seat weight sensor. The accelerometer outputis responsive to the amount of vertical acceleration caused by roadbounce acting on the vehicle seat and the weight sensor output isresponsive to the amount of force exerted downwardly on the vehicleseat.

A normalized measurement of seatbelt tension may be calculated by theprocessor by first calculating an average mass on the seat using theweight sensor output. The expected variation in force is then calculatedby multiplying the aforementioned average mass on the seat by the actualacceleration as measured by the accelerometer over a pre-determined timeperiod. A normalized seatbelt tension may then be calculated by dividingthe variation in force as measured by the seat weight sensor over apredetermined time period by the expected or calculated variation inforce over the aforementioned period.

The resultant scalar tension measure will approximate unity for unbeltedor loosely belted occupant situations where the mass acting on the seatis free to travel vertically. Accordingly, the normalized tension scalarwill decrease when extremely high belt tension is present therebyforcing the mass onto the seat.

Alternatively, the processor may calculate an expected force exerted onthe seat due to road-induced vehicle bounce at discrete time intervals,assuming that no belt tension exists, and compare the results with themeasured force exerted on the seat at the each discrete point in time.The ratio between the measured force and the calculated or expectedforce exerted on the seat provides an indication of belt tension.

Known seat weight sensors may comprise one or more pads employing forcesensitive resistive (FSR) elements disposed within the seat to provide aweight measurement. These arrangements are typically used as weightthreshold systems that are used in conjunction with a processor todisable a passenger air bag when the seat is empty.

Conventional load cells attached to the seat mounting posts have alsobeen used in research applications. The use of load cells as weightmeasurement means in the instant invention requires that the seatbeltsor passenger restraints are not mounted directly to the vehicle seatbecause a load cell system that weighs the entire seat and its contentsincluding the seatbelts and their mounting points will not be responsiveto the force applied to the seat by the tension in the seatbelt.

Mechanisms employing string actuated potentiometers to measure downwardseat displacement have also been utilized as weight measurement means.In these mechanisms, a weight resting upon a seat pad causes the pad tosag or curve downwardly, thereby displacing a string that is positionedacross the bottom of the seat pad. One end of the string is connected toa potentiometer shaft that is rotated when the string is displaced. Therotation of the potentiometer shaft causes the resistance at thepotentiometer output to change. A processor is adapted to measure thechanging resistance at the potentiometer output, thereby providing asignal proportional to string displacement, and therefore, the forcecaused by a mass present on the seat.

Copending U.S. Application Ser. No. 08/993,701 further discloses aweight sensor employing a gas filled bladder disposed within the seatpad to calculate seat weight. When a load is applied to the seat adifferential pressure sensor operatively coupled to the bladdergenerates a signal that is responsive to the pressure on the fluidwithin the bladder and therefore indicative of the force acting upon theseat. A signal processor having an input operatively coupled to thepressure sensor then calculates the force exerted on the seat as well asthe mass present.

By determining the amount of mass present in a vehicle seat and theamount of tension present in a passenger restraint belt, correctiveaction may be taken to further protect a vehicle occupant by adaptingother restraint system components, such as the air bag control system.

The ability to sense the tension present in a seat belt may be used inconjunction with a seat weight sensor to determine the presence of anoccupant in a vehicle seat and the relative size of the occupant. Thisinformation may be used either to deactivate seatbelt pretensioners,and/or modify the inflation profile of an air bag.

Furthermore, by sensing the amount of tension present in the seat belt,the deployment of an airbag may be inhibited in the presence of infantseats or in situations where occupants are small so as to reduce theirrisk of injury from the inflating air bag. Therefore, a system that canreliably predict the amount of tension present in a seat belt may beused to great advantage in vehicle safety systems.

One significant advantage of the instant invention is that it does notrequire numerous ancillary components that are in direct contact withthe seat belt system. The present invention can predict whether there issignificant tension in the seat belt without directly measuring seatbelt tension.

Therefore, one object of the instant invention is to provide a seat belttension measurement system that does not require a mechanism in directcontact with the seat belt or its associated assembly.

Another object of the instant invention is to use road-induced verticalacceleration exerted on every vehicle as a forcing function for a seatweight sensor signal. The oscillation of an accelerometer signalcompared with the oscillation of a weight sensor signal at discrete timeintervals provides the data required to calculate seat belt tension.

A yet further object of the present invention is to provide a seat belttension prediction system that requires minimal additional componentsbeyond a seat weight measurement means and the attendant processoradapted to receive and process various vehicle instrumentation signals.The instant invention requires only an accelerometer or equivalentacceleration sensing device and a conventional microprocessor orequivalent processing means in conjunction with a seat weight sensor toaccurately calculate seat belt tension.

A yet further object of the instant invention is to provide a seat belttension prediction system that is useful in determining the presence ofan infant seat in a vehicle. The present invention measures thecomponent of force acting on a vehicle seat that is attributable totension in the seat belt as well as the component of force attributableto the presence of a mass on the seat, thereby providing a means topredict whether the occupant is an adult or a child.

The instant invention will be more fully understood after reading thefollowing detailed description of the preferred embodiment withreference to the accompanying drawings. While this description willillustrate the application of the instant invention in an automotivesafety restraint system, it will be readily understood by one ofordinary skill in the art that the instant invention may also beutilized in other tension measurement systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatical view of a preferred embodiment of the instantinvention.

FIG. 2 is a diagrammatical view of an alternative seat weight sensorarrangement taken along the line 2—2 of FIG. 1.

FIG. 3 is a diagrammatical view of an alternative embodiment of theinstant invention.

FIG. 4 is a diagrammatical view of an alternative embodiment of theinstant invention.

FIG. 5 is a view of the instant invention taken along the line 5—5 ofFIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to FIG. 1, a seat belt tension prediction system and method 10for a vehicle 12 having a seat 14 is comprised of an accelerometer 20and a seat weight sensor 30. The accelerometer 20 is provided with anoutput signal 22 that is responsive to the amount of verticalacceleration acting upon the vehicle 12 and, therefore, on the vehicleseat 14. The accelerometer 20 must be rigidly secured to a vehiclestructural member 16 that experiences the same vertical accelerationthat the vehicle seat 14 is subjected to when traversing variations interrain. In a preferred embodiment of the instant invention theresolution of the accelerometer 20 is greater than 0.005 g to providesufficient sensitivity to small variations in vertical acceleration.

The seat weight sensor 30 is provided with an output signal 32 that isresponsive to the amount of force exerted downwardly on the vehicle seat14. Accordingly, the seat weight sensor output signal 32 will also beresponsive to additional force upon the vehicle seat 14 exerted bytension in a seat belt 34. The output signal 32 from the weight sensor30 must have an update period small enough to allow the weight sensor 30to sense oscillations in force on the seat 14 caused by the vehicle'svertical acceleration. In a preferred embodiment of the instantinvention the update period of the weight sensor output signal 32 isless than 25 milliseconds. Additionally, the weight sensor output signal32 may be AC coupled to filter low frequency signal oscillations thatnormally occur as a result of occupant movement, thus ignoring thoseoscillations that are not produced by road-induced verticalacceleration.

Furthermore, a processor 50 is provided, having a first input 52operatively coupled to the accelerometer output signal 22 and a secondinput 54 operatively coupled to the seat weight sensor output signal 32.The processor 50 is further operatively coupled to a vehicle airbagcontrol system 60 whereby the processor 50 may provide an output signal56, or a plurality thereof, to the airbag control system 60 to inhibitdeployment of an airbag and/or to modify its inflation profile.

The processor 50 may comprise an analog or digital microprocessor or anyequivalent thereof. Although the preferred embodiment of the instantinvention utilizes a conventional digital microprocessor, it is readilyunderstood by one having ordinary skill in the art that alternativemeans such as relay logic circuitry, analog processors, analog todigital converters and TTL logic circuitry may be employed as processormeans to practice the instant invention.

In an alternative embodiment of the instant invention shown in FIG. 2,seat weight sensor 40 comprises a plurality of force sensitive resistiveelements 42 disposed within the vehicle seat 14 for measuring force. Theforce sensitive resistive elements 42 provide as an output signal 44 avariable electrical resistance responsive to the amount of force actingon the elements 42, that may be operatively coupled to the input 54 ofprocessor 50. The variable resistance output signal 44 is generallyinversely proportional to the amount of force acting on the seat 14.

Referring to FIG. 3 and as disclosed in U.S. application Ser. No.08/993,701, a hydrostatic seat weight sensor 70 as incorporated in analternative embodiment of the instant invention, comprises a gas filledbladder 72 mounted within the vehicle seat 14 and a differentialpressure sensor 74 operatively coupled to the bladder 72 for measuringthe difference in pressure between the bladder 72 and the atmosphere.The differential pressure sensor 74 provides a pressure sensor output 76that is responsive to the force exerted downwardly on the seat 14. Thedifferential pressure sensor output 76 is operatively coupled to input54 of processor 50 thereby providing an indication of the force actingdownwardly on the seat 14.

As shown in FIG. 4, an alternative seat weight sensor comprises aplurality of load cells 80 disposed between the vehicle seat 14 and thevehicle structure 16 such that the entire weight of the seat 14 restsupon the load cells 80. The load cells 80 are provided with an output 82that is responsive to the amount of force acting upon the seat 14. Whenutilizing load cells 80 as a weight sensors, it is critical that theseat belt 34 is mounted to the vehicle 12 such that load cell 80 isresponsive to the force upon the seat 14 generated by tension present inthe seat belt 34. For example, FIGS. 4 and 5 provide illustrations of aseat belt 34 configuration wherein the load cells 80 are responsive toboth the tension applied by the seat belt 34 and the force resultingfrom a mass resting on the seat 14.

In operation, and in accordance with the preferred embodiment of theinstant invention, the accelerometer 20 measures the verticalacceleration of the seat 14 and provides an output signal 22 to theprocessor 50. A normalized seatbelt tension measure is then calculatedby the processor 50 to detect high belt tension and thereby determinethe presence of a child seat.

The processor 50 is programmed to calculate an average mass of an objectresting on the seat by dividing the output 32 of the weight sensor 30 bythe earth's gravitational constant, g. This calculation may be performedat a predetermined time during the operation of the vehicle 12, orpreferentially, performed continuously by assuming that the verticalacceleration of the vehicle 12 and the belt tension are negligible, andaveraging the resultant successive mass calculations.

A predicted variation in force exerted on the seat 14 is calculated inthe processor 50 by multiplying the aforementioned average mass by themeasured variation in vertical acceleration as provided by theaccelerometer 20 over a predetermined time period. The variation invertical acceleration over time may be determined by integrating theabsolute value of the difference between the accelerometer output 22 andthe earth's gravitational constant g over the aforementioned timeperiod.

The variation, or fluctuation of the actual force exerted on the seat 14is then determined by integrating the absolute value of the differencebetween the seat weight sensor output 32 and the average force exertedon the seat 14. The normalized tension measurement is then calculated bydividing the variation in actual force exerted on the seat over the sametime period as measured by the weight sensor 30, by the predictedvariation in force exerted on the seat 14. The time period over whichthe predicted force variation is calculated must be sufficient to allowroad induced bounce to impart vertical acceleration to the vehicle 12.In a preferred embodiment of the instant invention the time period usedto calculate the normalized belt tension is .5 seconds.

In an alternative embodiment of the instant invention the processor 50calculates the force exerted downwardly on the seat 14 at discrete timeintervals utilizing the vertical acceleration measurement provided bythe accelerometer 20, and assuming that no seat belt 34 tension ispresent in the system, and then compares the resultant predicted forcewith the actual measured force at each discrete point in time tocalculate belt tension. As an example, the predicted force acting on theseat 14 may be calculated by programming the processor 50 to perform thefollowing algorithm:F=M(g−A)+BT,where

-   -   F is the force acting downwardly onto the seat 14,    -   M is the mass of the object on the seat 14,    -   g is the gravitational acceleration exerted on the mass M by the        earth,    -   A is the vertical acceleration of the vehicle 12, excluding the        earth's gravity, and    -   BT is the vertical component of the tension present in the belt        34.

The vertical acceleration A of the vehicle 12 fluctuates around zero andthus causes variations in the force F acting on the seat 14. The belttension BT approximates a constant value that is near zero for mostoccupant seating situations except for the presence of tightly beltedchild seats. The belt tension BT is generally a small value because belttension greater than a few pounds of force has been found to beuncomfortable for most vehicle occupants thereby making it unlikely thatan occupant is present when there is significant tension in the seatbelt 34.

As previously disclosed, the output signal 32 of the weight sensor 30 isdivided by the earth's gravitational constant g by processor 50 tocalculate the average mass M present in the vehicle seat 14. Theprocessor 50 then calculates a predicted force acting downwardly on theseat 14 at discrete time intervals using the aforementioned averagemass, with the assumption that the belt tension BT is zero. Stillassuming zero belt tension BT, the processor 50 then compares the actualvalue of the force F as measured at each discrete point in time by theweight sensor 30 with the calculated or predicted force. The differencebetween the predicted and actual values of force F provides anindication of the tension present in the belt BT.

In an alternative method for predicting belt tension BT, the processor50 monitors the weight sensor output signal 32 at discrete timeintervals and measures the amplitude of the oscillations of the outputsignal 32 at each discrete point in time. The processor 50 furthermonitors the accelerometer output signal 22 at the correspondingdiscrete time intervals and calculates the amplitudes of theoscillations of the accelerometer output signal 22. The resultantaccelerometer amplitude measurements are then sequentially multiplied bythe average mass M present in the vehicle seat 14 to calculate thepredicted force acting on the seat 14 at each discrete point in time.The ratio of the actual force acting on the seat 14 to the calculatedforce at each time interval thereby provides a measure of seat belttension.

A tightly belted mass present in the vehicle seat 14 will produce areduced ratio of actual force to predicted force as compared to theratio calculated when a “free” mass is positioned in the vehicle seat14. Therefore, the smaller the ratio between actual force as indicatedby the weight sensor 30 to predicted force as calculated using theaverage mass M and the accelerometer output signal 22, the greater thebelt tension BT, and the higher the probability that an infant seat istightly belted down onto the vehicle seat 14. The processor 50 may beprovided with a look-up table whereby seat belt 34 tension may bedetermined given a specific calculated tension ratio.

Accordingly, and as shown in FIG. 1, where the processor 50 calculates alevel of tension in the seat belt 34 in excess of a predeterminedmaximum, the processor 50 will generate an output 56 operatively coupledto an air bag control system 60 to inhibit deployment of the air bag.Alternatively, where the processor 50 calculates a level of tension inthe seat belt 34 below the predetermined maximum and the seat weightsensor 30 indicates that the occupant's weight is below a predeterminedminimum, the processor 50 will provide an output 56 to the air bagcontrol system 60 to reduce the inflation profile thereof according tothe measured weight of the occupant.

While specific embodiments of the instant invention have been describedin detail, those with ordinary skill in the art will appreciate thatvarious modifications and alternatives to those details could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangements disclosed are meant to beillustrative only and not limiting as to the scope of the invention,which is to be given the full breadth of the appended claims and any andall equivalents thereof.

1. A system for measuring seat belt tension in a vehicle having anairbag control system and a seat, comprising: a.) an accelerometerrigidly secured to said vehicle in proximity to the seat thereof, saidaccelerometer having an output signal responsive to the verticalacceleration of said vehicle; b.) a seat weight sensor having an outputsignal responsive to the force exerted by a mass on said seat; and c.) acomputer processor having first and second inputs, the first input beingoperatively coupled to the output signal of said accelerometer and thesecond input being operatively coupled to the output signal of said seatweight sensor, wherein said processor calculates tension in said seatbelt by comparing the output signal of said seat weight sensor atdiscrete time intervals with predicted fluctuations in the force exertedon the seat caused by vertical acceleration acting upon the mass,assuming no seatbelt tension.
 2. The system of claim 1 wherein said seatweight sensor comprises a hydrostatic seat weight sensor disposed withinthe seat.
 3. The system of claim 1 wherein said seat weight sensorcomprises a plurality of load cells adapted to be responsive to theforce exerted on the seat by said seat belt.
 4. The system of claim 1wherein said seat weight sensor comprises a plurality of force sensitiveresistive elements disposed within the seat.
 5. The system of claim 1wherein said computer processor further comprises an output operativelycoupled to said air bag control system for inhibiting said controlsystem upon the calculation of high seat belt tension.
 6. The system ofclaim 2 wherein said computer processor further comprises an outputoperatively coupled to said air bag control system for inhibiting anoperation thereof upon the calculation of high seat belt tension.
 7. Thesystem of claim 3 wherein said computer processor further comprises anoutput operatively coupled to said air bag control system for inhibitingan operation thereof upon the calculation of high seat belt tension. 8.The system of claim 4 wherein said computer processor further comprisesan output operatively coupled to said air bag control system forinhibiting an operation thereof upon the calculation of high seat belttension.
 9. A method for predicting seatbelt tension in a vehicle havinga seat, an accelerometer rigidly secured to said vehicle in proximity tothe seat, said accelerometer having an output signal responsive to avertical acceleration of said vehicle, a seat weight sensor having anoutput signal responsive to a force exerted by a mass acting on theseat, and a processor having a first input operatively coupled to theoutput signal of said accelerometer and a second input operativelycoupled to the output signal of said weight sensor comprising: a.)measuring an actual variation in force due to vertical accelerationexerted on the seat over a predetermined time period; b.) calculating anaverage mass on the seat; c.) calculating a predicted variation in forcedue to vertical acceleration exerted on the seat by multiplying theaverage mass on the seat by the variation in vertical acceleration overa predetermined time period; and d.) dividing the actual variation inforce by the predicted variation in force whereby a quotient representsnormalized seatbelt tension.
 10. A method for predicting seatbelttension in a vehicle having a seat, an accelerometer rigidly secured tosaid vehicle in proximity to the seat, said accelerometer having anoutput signal responsive to a vertical acceleration of said vehicle, aseat weight sensor having an output signal responsive to a force exertedby a mass on the seat, and a processor having a first input operativelycoupled to the output signal of said accelerometer and a second inputoperatively coupled to the output signal of said weight sensorcomprising: a.) measuring the force due to vertical acceleration exertedon the seat at discrete time intervals; b.) calculating an average masson the seat; c.) calculating at discrete time intervals a predictedforce acting on the seat due to vertical acceleration, assuming thetension in said seat belt is zero; and d.) calculating at discrete timeintervals a difference between the measured force exerted on the seatand the predicted force whereby the difference is indicative of seatbelt tension.
 11. A method for predicting seatbelt tension in a vehiclehaving a seat, an accelerometer rigidly secured to said vehicle inproximity to the seat, said accelerometer having an output signalresponsive to a vertical acceleration of said vehicle, a seat weightsensor having an output signal responsive to a force exerted by a masson the seat, and a processor having a first input operatively coupled tothe output signal of said accelerometer and a second input operativelycoupled to the output signal of said weight sensor comprising: a.)measuring the force due to vertical acceleration exerted on the seat atdiscrete time intervals; b.) calculating an average mass on the seat;c.) measuring the vertical acceleration acting on said vehicle atdiscrete time intervals; d.) calculating at discrete time intervals apredicted force exerted on the seat by multiplying the verticalacceleration at each time interval by the average mass, assuming thetension in said seat belt is zero; and e.) calculating at discrete timeintervals a ratio between the measured force exerted on the seat and thepredicted force exerted on the seat whereby the ratio is indicative ofseat belt tension.
 12. A system for controlling the actuation of arestraint actuator in a vehicle, comprising: a.) an accelerometeroperatively coupled to the vehicle, wherein said accelerometer generatesa first signal responsive to a vertical acceleration of the vehicleproximate to a seat thereof, wherein said seat is associated with therestraint actuator; b.) a force responsive sensor operatively coupled tosaid seat, wherein said force responsive sensor generates a secondsignal responsive to a weight on said seat; and c.) a processoroperatively coupled to said accelerometer and to said force responsivesensor, wherein said processor is adapted to generate a third signal forcontrolling the actuation of the restraint actuator, and said thirdsignal is responsive to both said first signal and said second signal.13. A system for controlling the actuation of a restraint actuator in avehicle as recited in claim 12, wherein said accelerometer is rigidlysecured to the vehicle in proximity to said seat.
 14. A system forcontrolling the actuation of a restraint actuator in a vehicle asrecited in claim 12, wherein said force responsive sensor comprises ahydrostatic seat weight sensor disposed within said seat.
 15. A systemfor controlling the actuation of a restraint actuator in a vehicle asrecited in claim 12, wherein said force responsive sensor comprises aplurality of load cells adapted to be responsive to the force exerted onsaid seat responsive to a seat belt associated therewith.
 16. A systemfor controlling the actuation of a restraint actuator in a vehicle asrecited in claim 12, wherein said seat weight sensor comprises aplurality of force sensitive resistive elements disposed within saidseat.
 17. A system for controlling the actuation of a restraint actuatorin a vehicle as recited in claim 12, wherein said third signal isresponsive to whether the mass on the force sensor is free to travelvertically.
 18. A system for controlling the actuation of a restraintactuator in a vehicle as recited in claim 12, wherein said third signalprovides for discriminating a tightly belted mass on said seat.
 19. Asystem for controlling the actuation of a restraint actuator in avehicle as recited in claim 12, wherein said third signal provides forpredicting whether an occupant on said seat is an adult or a child. 20.A system for controlling the actuation of a restraint actuator in avehicle as recited in claim 12, wherein said restraint actuatorcomprises an air bag.
 21. A method of controlling the actuation of arestraint actuator in a vehicle, comprising: a.) generating a firstsignal responsive to a vertical acceleration of the vehicle proximate toa location of a seat, wherein said seat is associated with the restraintactuator; b.) generating a second signal responsive to a weight uponsaid seat of the vehicle; and c.) controlling the actuation of therestraint actuator responsive to said first and second signals.
 22. Amethod of controlling the actuation of a restraint actuator in a vehicleas recited in claim 21, wherein the operation of controlling theactuation of the restraint actuator comprises: a.) determining anaverage mass on said seat from said second signal; b.) determining afirst variation responsive to a plurality of said second signals withina time period; c.) determining a second variation responsive to aplurality of said first signals within said time period; and d.)determining a quotient responsive to a division of said first variationby said second variation and by said average mass, wherein the operationof controlling the actuation of the restraint actuator is responsive tosaid quotient.
 23. A method of controlling the actuation of a restraintactuator in a vehicle as recited in claim 21, wherein the operation ofcontrolling the actuation of the restraint actuator comprises: a.)determining an average mass on said seat from said second signal; andb.) determining a quotient responsive to a division of a measureresponsive to said second signal by a measure responsive to said firstsignal and by said average mass, wherein the operation of controllingthe actuation of the restraint actuator is responsive to said quotient.24. A method of controlling the actuation of a restraint actuator in avehicle as recited in claim 22, wherein the actuation of the restraintactuator is inhibited if said quotient is less than a threshold.
 25. Amethod of controlling the actuation of a restraint actuator in a vehicleas recited in claim 23, wherein the actuation of the restraint actuatoris inhibited if said quotient is less than a threshold.
 26. A method ofcontrolling the actuation of a restraint actuator in a vehicle asrecited in claim 21, wherein the operation of controlling the actuationof the restraint actuator comprises: a.) determining an average mass onsaid seat from said second signal; and b.) determining a differencebetween a measure responsive to said second signal and a product of saidaverage mass and a measure responsive to said first signal, wherein theoperation of controlling the actuation of the restraint actuator isresponsive to said difference.
 27. A method of controlling the actuationof a restraint actuator in a vehicle as recited in claim 26, wherein theactuation of the restraint actuator is inhibited if the magnitude ofsaid difference is greater than a threshold.
 28. A method of controllingthe actuation of a restraint actuator in a vehicle as recited in claim21, wherein said first and second signals are generated as discrete timeintervals.
 29. A system for controlling the actuation of a restraintactuator in a vehicle as recited in claim 21, wherein said restraintactuator comprises an air bag.